The Experiment
by HazelHype
Summary: She was a failed Kraang experiment, destined to be terminated. But with her only friend, Leatherhead, to help her, she escapes into Dimension X. Before he is captured, he tells her to wait for "the turtles", whatever that means. Mostly Donnie/OC cuz I think Rob Paulsen is awesome.
1. Into Dimension X! Part 1

Whatever she was, she knew what she wasn't. And she wasn't their slave. Any clues from the Kraang on what she was were very cryptic. They had simply referred her as "the vulpes-hybrid". Kasha, a name given to her by her only friend, Leatherhead, ran along side him as they attempted their escape plan. They were finally getting away from the Kraang.

A glass wall stood between them and freedom. Kasha inhaled deeply and let out a super sonic scream that shattered the glass. Once the glass was gone, they jumped out and landed on one of the metal lands, at least, that's what Kasha called them. Leatherhead gathered her up and had her hold on to his back while he ran through the crystal jungle. He carried a crystal club in one hand and a communication orb in the other. Once they stopped, Kasha slid off of her friend's back. Her whiskers twitched as she sniffed the air. "If you plan to contact them, now is your only chance." She said as she turned to her friend.

The mutant alligator nodded as he spoke to the beeping orb. "Turtles. The Kraang have perfected the mutagen. They're about to-" he stopped mid-sentence when he heard something. Turning to Kasha, he gave her his club. "Run, Kasha. You must guide them if they come."

Kasha let a lone tear fall from her eye as she nodded. She silently ran until she came to the edge of the metal land. Turning back, she saw Kraang bots approaching. Not giving them time to speak, she jumped off the edge and hurled herself to the next bit of metal land. She kept running until she knew they were no longer chasing her.

* * *

Kasha started to fear that Leatherhead's friends were never going to come. Weeks passed and her only source of food was hunting stray Kraang. It felt good to hunt them, making them feel like prey.

She combed her fingers through the fur of her tail nervously, still not know what she was. Looking at her reflection on the wall she was leaning against, she looked at her orange and white fur. Her ears stuck out and were pointed with black tips. She still remembered that the Kraang called her "vulpes-hybrid", whatever that was. She just hoped that she knew what she was soon or she'd go insane.

* * *

It had been so long since Leatherhead sent the message. Just as Kasha was having doubts, she saw one of the rock-hoppers chasing a strange green creature that wore an orange mask. His screams were high pitched as he ran away from the rock-hopper. Kasha jumped to the metal land that the chase was happening on and sceeched as loud as she could, scaring it enough to make it stop. She then jumped on top of it and punched its feeler, the tiny head with green eyes, causing the monster to fall back in fear.

The green creature stared at Kasha in awe. "You totally saved me. Thanks."

"What are you?!" She demanded as she approached him with Leatherhead's crystal club. "In all my years living in this cursed place, I have never seen a creature like you!"

"I'm a turtle, dudette. The teenage mutant ninja variety." He answered. "The name's Michelangelo, but you can call me Mikey."

Kasha lowered the club upon hearing this. "Turtle? Are you one of the creatures Leatherhead was trying to contact?"

"Leatherhead! Where is he?" The Mikey asked.

"He was recaptured by the Kraang. But we need more than two of us to rescue him." Kasha said. Suddenly, the rock-hopper appeared again and Kasha gave it a warning growl to scare it off. "We need to go or else that thing will try to eat us." She then led Mikey to her own little camp on a different metal land.

"So, are you like a fox-girl or something?" Mikey asked.

"What is a 'fox'?" Kasha asked.

"They're these cute little dog things that yip instead of bark and do these adorable jumps and stuff." Mikey explained.

Kasha stared at Mikey like he was insane. "I can assure you that I am not adorable or cute. I am strong, hearty and very aggressive. And it seems that I will have to teach you to be that, as well."

* * *

Months had passed. Kasha taught Mikey everything she knew about Dimension X. And while scouting the H.Q. and taking down a few lone Kraang, Kasha helped Mike make a mask and belt from one, explaining that he needed to be visually intimidating as well as vocally.

One day, after they picked some bang-rocks, Mikey saw his brothers. They were being chased by a rock-hopper, or as he called them, a rocktopus. "My brothers are here!" He yelled. He was quick to grab a rope-tongue slug and swing his way to his brothers' rescue. After he pulled them from harms way and threw some bang-rocks, Kasha swung in and pulled them further away to give Mikey some room.

They struggled at first, but stopped when she yelled, "If you value your lives and that of your brother's, you will do what I say!" They then followed her as Mikey swung himself up and kicked the rock-hopper's feeler, sending it over the side of the metal land.

"You're okay!" The purple-clad turtle exclaimed.

"We were worried about you." The blue one added.

"Well, what took you so long?" Mikey asked. "I've been here for months."

"Months?" The blue turtle asked.

"Or maybe a few hours. I don't have a watch." Mikey added.

"But we went through the portal, like, fifteen seconds behind you." The red-clad turtle said.

"Obviously, time passes faster here than it does in our own dimension. There's a temporal differential." The purple turtle explained.

"I love temporal." Mikey smiled. He then motioned for Kasha to join them. "Guys, this is Kasha. She totally saved my shell when I first got here. She taught me everything about Dimension X, and she's also the reason I was able to survive here." He then turned to Kasha. "Dudette, these are my bros. Leo, the leader. Donnie, the genius. And Raph, the hothead."

"Hey!" Raph yelled.

"It is an honor to meet all of you. Mikey speaks so fondly of his family."

"How are you able to breathe this atmosphere?" Donnie asked.

"I'm a failed Kraang experiment. They spliced their DNA with another race of alien, in hopes of creating a protector of Kraang Prime. Unfortunately for them, my will was never broken." Kasha explained before seeing the rock-hopper return. Both she and Mikey screeched at it, sending it back in fear.

Donnie was confused by this. "Wait. How did you-"

"Let's get moving. That thing's gonna keep coming back. And we gotta rescue Leatherhead." Mikey explained.

"Stock up on bang-rocks before we head out." Kasha told him.

Mikey nodded before jumping on a crystal tree. "Mikey, be careful!" Donnie yelled. The orange turtle ignored his brother as he lightly howled at a few low hanging crystals. They popped right off, his for the taking. "How did you do that?"

"A lot of stuff here responds to sound." Mikey said before jumping down to his brothers. He then picked up some rope-tongue slugs and handed them to his brother.

"What are we supposed to do with these?" Leo asked.

"Like this." Mikey said. He then gently squeezed the slug to srnd out its tongue to a drifting piece of land. Kasha did the same. The brothers shrugged before bollowing suit. Unfortunately, they didn't realize how strong the pull was going to be.

After they crashed on the land, Kasha and Mikey followed, landing on their feet.

"Woah, how'd you know how these bug things worked?" Raph asked.

"Kasha showed me." Was Mikey's answered.

"Mikey, you're like a genius here." The red turtle added.

"Hey, in 'crazy-backwards land', 'crazy-backwards dude' is king." Mikey said before squeezing his rope-tongue slug to get the nectar it secreted. "They're tasty, too." But his brothers looked as though tjey were going to be sick. Mikey ignored them as he exclaimed, "Now, let's go rescue Leatherhead!"

* * *

 **Hi. Hope this is a good start. Plz review ㈳3**


	2. Into Dimension X! Part II

Mikey and Kasha led the three older turtles to the Kraang Facility. Mikey's brothers snuck up on foot while Mikey swung from his rope-tongue slug and Kasha silently jumped from one crystal branch to another, still carrying Leatherhead's crystal club. Her ears perked when she the guardians begin to stir. They could hear the heroes coming. She signaled for Mikey to let his brothers know about the stone titans.

"Okay, I got some good news and I've got some bad news." He said.

"What's the good news?" Leo asked.

"There's thousands of Kraang droids in there." Mikey answered.

"I said 'good' news." The blue turtle said.

"I know." Mikey responded. As if on que, the stone giants came out of hiding, much to the skock of the newly-arrived turtles. "That's the bad news." Mikey said.

The white titan blew out blue fire from its mouth while the back one spewed out lava from its own. The attack was on. Just as Mikey and Kasha were about to take care of them, the other three turtles had their own ideas.

After a few minutes of getting their shells handed to them, Leo was picked up by the black giant. Mikey just couldn't take it anymore. "Hey, Dreg! Granitor! Put him down! Now!" Mikey then threw a fist-full of bang-rocks at the giants, causing Granitor to drop Leo. Once out of the way, Mikey went into full on offence. "I told you, we got this."

Both Mikey and Kasha cornered the giants to the edge of the metal land before the turtle nodded to the hybrid. Kasha took a bracing stance and took in a deep breath before releasing a sonic roar, making the whole land shake. The weight from the giants proved too much and the edge of the land broke off, taking the giants down with it.

Kasha was gasping, trying to catch her breath before turning to face the older turtles. She saw that they were staring wide-eyed. "What?"

"That was incredible." Donnie said.

"Amazing." Leo added.

"What was that weird scream?" Raph asked.

"Sonic Roar." Kasha answered. "One of my more powerful abilities. But it takes a lot out of me. So I only use it when I have no other choice." She was able to steady her breath before continuing. "Any other abilities you happen to be curious about will have to wait. We need to rescue Leatherhead."

"She's right." Mikey agreed. "Let's move!" And they followed the youngest turtle into the building.

Once inside, the turtles followed Kasha. She easily picked up on her friend's scent. Finding his cell was easy, she just followed his scent. She saw one particular set of doors covered in Leatherhead's scent, but they were being guarded by two Kraang in Kraang Bots. Leo was prepared to fight them, but Mikey stopped him before bringing out two rope-tongue slugs. He then squeezed their tongues out to pull the Kraang from the bots, making them defenseless. Once on the ground, the two Kraang looked up to find Kasha staring down at them, growling low. They tried to squirm away, but Kasha kicked them to the wall with enough force to knock them out.

"Smooth." Raph smirked.

Looking through the window in the door, the turtles and Kasha saw a tree in the middle of the room. "Initiate that which is called mutigen transformation sequence." One of the Kraang said

"That which is called mutigen transformation sequence initiated." Another Kraang confirmed. They then sprayed a tree down with mutigen, turning it into a crystal structure. The Kraang vacated the room and the mutants enter to get a closer look.

"So that's what Leatherhead meant when he said they perfected the mutigen. They're gonna use it to transform everything on Earth, even the people. They're gonna turn Earth into another Dimension X." Donnie explained.

"So I'll be a genius there, too?" Mikey asked as he stared at the crystal structure.

"Yes, Mikey." Donnie answered with sarcasm. "Thank you for finding the one mildly positive thing among TEN BILLION SCREAMING NIGHTMARES!"

Kasha suddenly shot her hand up to cover Donnie's mouth. "Ssh!" She hissed. "Be silent. We don't know who could be listening." She then forced them to follow her down a hallway that wreaked of Leatherhead's scent. The further they ran, the sooner they heard the giant retile's screams of agony. Kasha's eye's widened with fear for her friend. She ran even faster till she found where he was being kept. He was locked in virtual cuffs that also secured his head and chained him down to kneel on the floor. Kasha saw red as she charged and destroyed both Kraang bots, leaving the turtles to take care of the little aliens.

"Leatherhead!" She gasped as she ripped the wiring out of the wall to free him of his confinements. He fell forward.

The three older brothers were in awe of her sudden super strength, suddenly looking at Mikey for an explanation. He just shrugged, saying, "In times of desperation, Kasha can do anything." He then joined her in helping their friend stand.

"Thank you, my friends." Leatherhead coughed. "I feared you would never come."

"Dude, did you quit morsturizing or something? You look a ton older." Mikey stated.

"It's the temporal differencial, Mikey." Donnie explained.

"Yes." The giant mutant confirmed. "I have been in this place for may decades now, spying on the Kraang. When I found Kasha, she was able to tell me everything they were doing. Even when they were trying to perfect the mutagen. I had to contact you when the finally succeeded. Now that the time has come, their invasion begins now." He then took back his club from Kasha. "Follow me!" He growled. He ran out of the room and roared at one of the Kraang that remained on the floor, causing it to tumble away.

Everyone was shaken up by this sudden aggression, but it was understandable to Kasha. She had bee at the mercy of the Kraang her entire life. She would have done the exact same thing. "He's a little cranky." Mikey whispered to his brothers.

"But he's right. We have to stop the invasion." Kasha conquerred as she followed her friend.

The turtles were quick to follow and soon, the hallway lead to a giant room were a huge power crystal was being used to power a portal generator. "Oh, that's not good." Donnie stated.

"So many portals." Leo noted. "But why so many?"

"Look!" Leatherhead growled. The walls surrounding the room opened up to reveal many armies of Kraand bots.

Donnie nervously stepped back. "So, looks like we're done here."

"Those tunnels lead to the hive factorywhere the Kraand droids are manufactured. Their numbers are effectively limitless." Leatherhead explained.

This seemed to shake Donnie up. "So what can we do?"

"We can go down fighting." The giant said. "I would rather die on my feet than live on my knees."

"Well, I wouldn't. I have knee pads! The only sensable course of action is retreat!" Donnie exclaimed.

Kasha suddenly got angry. She grabbed to top of Donnie's plastron and shoved him against the wall. She bared her fangs and her eyes glowed in anger. Donnie had never been more afraid of a female in his life. Kasha then spoke in a dangerously low voice. "You would run like a coward while your planet suffers? Believe me when I say that what they are truly capable of runs far beyond mutation. And I would rather die than be tortured for a second longer by the Kraang." She then let him go and faced Mikey. "I trust your judgement, friend. And I will do whatever you task me with."

Mikey nodded and turned to face everyone. "Leo and Raph, block that tunnel! Donnie and I will sabotage the portal generator! And Leatherhead and Kasha-"

"Crush Kraang?" Leatherhead asked.

"A lot!" Mikey confirmed.

The turtles then swung out of the doorway with their rope-tongue worms while Leatherhead put Kasha on his back and dropped to the ground. Kashe leapt off of his back and tackled another bot, ripping it's head off and throwing it at another Kraang. One Kraang in particular shot blasts from its gun at her, and one shot grazed her left shoulder. She turned and glared at the alien before body started glowing. Her tail seemed to split into nine different tails and grow longer. Her now many tails started rubbing together and were lighting small balls of fire. They seemed to know where to go because they each hit any Kraang that was coming near her. She grabbed the Kraang that shot her and threw him into the air as high as ever. Then her tails created a lightning bolt that shot at the offending alien and fried it to a crisp. It then fell to the floor in a smoking heap.

Kasha's tails melded and shrank back into her normal tail. But she then collapsed and passed out. Leatherhead, after he threw Leo over a tripod to flip it over, faw Kasha and picked her up and held her over his shoulder. By this time, Mikey had managed to push Donnie away so he could open th eright portal and close all the rest. Leatherhead placed Kasha in Donnie's arms. Go, take her with you. I'll stay behind to fend them off."

"Not this time, buddy." Mikey said as he pushed his friend into the portal. The others followed close behind. With Mikey being the last. "Well, goodbye being smart." He said before jumping through. But one he crossed over he had the idea of getting a piece of the power crystal for Doniie's invention. Using his worm, he snagged a big piece and pulled it through just as the portal closed.

Donnie managed to hold Kasha with one arm while climbing the apartment building they landed on. Once on the roof he sat her down to see she was waking up. "Are you okay?"

Kasha blinked and nodded as she groaned. "What happened to me?"

I think it would be best if we talked to Splinter. He might be able to help up." Donnie said as he helped her stand. Still kind of wobbly, Kasha lost her ballance and fell on Donnie. both blushed but Kasha managed to get her footing back and stand without his help.

"Thank you for helping me save my friend. And for helping to stop the invasion." She said with a small smile.

"Hey, Donnie! Mikey said as he hung onto the side of the building. "I got you a new power source for you."

"Mikey, you are a genious." The smart turtle said.

"Not anymore." Mikey said as he removed his Kraang mask. "Now, I'm just back to being regular, mess-everything-up Mikey."

"No way." Leo said. "saving that power cell was brilliant. And you did that over here."

With a sudden confidence boost, Mikey smiled. "Yeah. Maybe I'm not such a screw up after all." he said as he rubbed the back of his neck with the hand that was holding him up. Suddenly realising his mistake, Mikey fell off the building. Kasha looked over the side, seeing that he was fine and sighe din relief.

"That overload should have taken out their whole facility. Their invasion will be set back for months." Donnie explained.

"Yeah, but how long is that with the whole time differencial thing?" Raph asked.

"I don't know." Donnie admitted. "Hours. Maybe a day."

"Guys, there's a storm coming. Are we ready to fight?" Leo asked.

Donnie, Raph and Leaytherhead were quick to agree. Kasha looked at the leader and nodded as she said, "With my life."

Everyone then turned to Mikey who seemed to be in his own world. "I need a minute." He said before openning his eyes. "Okay, now I'm ready. Booyakasha!" All mutants then high-fived, except for Kasha, who just smirked.

* * *

 **Hi. Hope this is a good so far. Plz review ㈳3**


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